I'm seeing two parts to this question: what does Uncle Sam want and what does Apple want.
Check the Small Business Administration for the legal/tax requirements of your state. It's a way powerful resource—use it to make sure Uncle Sam is happy.
As far as Apple goes—you don't need any special licenses to refurbish and sell. I'd make sure and restore/install the OS the device came with. And, as a general rule, make sure the end user does all the software setup themselves after the OS is installed. If they want to upgrade the OS from what the device was shipped with, let them do it themselves.